Zimbra + Evolution + calDAV

Hi everybody,

I'm trying to connect Evolution under Ubuntu 9.04 to a Zimbra Server CE 6.0.1. In Zimbra https encryption is enabled.
When defining a new Calendar in Evolution using the "caldav" protocol with an address like this:

caldav://server/dav/user/calendar

the existing calendar data are read and displayed correctly. But trying to add a new entry Evolution just sais "Unknown error" after clicking "save" and does not save the entry.

This is exactly the sort of behavior I'm getting on my home instance, which is FOSS. This is working at work, where we have the NE. I think the main difference, though, is that the home setup is a "hosted" domain. It's main configuration is the local network, but my account is in another hosted domain. I thought at first that the problem lie in having "@domain" in my URL, but I can take this out, and Evolution still can _read_ the calendar, but it still can't _write_. Any tips on how I can better configure this so that it will work?